Objective: Vitamin D plays a key role for children‘s growth and physical developement, not only by promoting bone health but also by its influence on extraskeletal systems. The Icelandic Directorate of Health recommends a vitamin D concentration in blood of at least 50 nmol/l. The object of this study was to evaluate the vitamin D status of Icelandic children and youngsters at four different ages, and furthermore to evaluate changes in vitamin D concentrations over time and connection to parathyroid hormone status (S-PTH).

Material and methods: The subjects were students from six elemen­tary schools in Reykjavík, born in 1999. Blood tests were taken four times, in 2006, 2008, 2015 og 2017. Some of the subjects took part in all four tests, but more students joined in 2015 and 2017.

Results: In all the tests, around 60% of the subjects had lower vitamin D concentrations than recommended by The Icelandic Directorate of Health. Only 13% met the recommended criteria of a concentration over 50 nmol/l in repeated tests and 38.9% of the subjects had lower concentrations than recommended in at least two tests. There was no significant difference between sexes except that 17 year old girls had significantly higher Vitamin D concentrations than boys (p=0.04). S-PTH was negatively correlated to vitamin D concentrations at ages 7, 15 and 17 but there was not a significant correlation at age 9. S-PTH values were lowest at age 7 and then increased with age.

Conclusion: The majority of Icelandic children and youngsters have vitamin D concentrations under the values recommended by The Icelandic Directorate of Health. In many cases, the concentrations are repeatedly too low. It is clear that there is a need for increased vitamin D intake within this group if the goal regarding recommended concentrations is to be achieved. However, the influence of vitamin D deficiency on public health is not fully known.

	Age (years)	Vitamin D N	Mean (SD) nmol/l	S - PTH N	Mean (SD) ng/l
Girls	7	86	46.6(14.4)	89	28.7(8.1)
	9	92	48.1(16.5)	100	36.6(12.4)
	15	163	43.3(23.2)	165	39.0(12.4)
	17	134	50.4(23.8)	134	40.2(13.5)
Boys	7	73	48.4(13.8)	73	24.9(7.5)
	9	61	47.6(16.1)	66	35.2(13.3)
	15	119	41.7(22.7)	119	41.9(14.1)
	17	78	44.4(18.7)	78	43.0(23.7)

Table I. Mean values for vitamin D concentrations and S-PTH in blood divided by age and gender.